Electron-discharge apparatus



A ril 29, 1930. H. c. THOMPSON ELECTRON DISCHARGE APPARATUS Filed Dec. 14, 1927 Inverwtcn- Harry C .Thompson V by His Attorney.

Patented Apr. 29, 1930 UNITED STATES HARRY C. THOMPSON, F SCHENECTADY, NEW YORK, ASSIGNOR '10 GENERAL ELEG- TBIC COMPANY, A CORPORATION OF NEW YORK ELECTRON-DISCHARGE APPARATUS Application filed December 14, 1927. Serial no.

My present invention relates to electron discharge apparatus, and more particularly to apparatus of the type in which advantage is taken of the capabilites of an electrode to emit secondary or impact electrons.

It has heretofore been proposed to operate electron discharge devices having an electron emitting cathode, and'two or more other electrodes, with such circuit connections that emission of impact electrons from one of the electrodes, may be obtained of sufficient amount to give the device a negative resistance characteristic, thereby enabling it to be utilized efliciently as an amplifier or generator of high frequency currents.

One of the objects of my invention is to I provide an apparatus of the character described in which the electrode which emits impact electrons is capable of doing so more effectively than those heretofore known.

Still another object of my invention is to provide an improved method for coating the surface of such an electrode so that it will be e flicient as an emitter of impact electrons, and

5 its property in this respect will remain substantially unchanged over a long period of operation.

I have found that the impact emitting "Property of an electrode may be gr atl aolhancedby forming on the electrode a suitable coating of a compound of a metal having alkaline properties. It is of course necessary that a compound be chosen which will be stable during the conditions of operation so that the emitting properties ofthe elec trode will not vary materially over a long period. Among the compounds which seem the most suitable for this purpose are borates and oxides. I have found that very good results may be obtained by the use of borates of potassium, lithium, sodium, barium, magnesium and oxides of barium, strontium and calcium. Some of these compounds are stable 1;; when used in an evacuated receptacle, al-

though ey are subject to change when exposed to the air.

In some cases it is desirable to use a compound which is reduced to a difl'erent form by the a plication of heat. I have also found it desira le to supply to the electrode during the process of manufacture of the device the vapor of a metal having alkaline properties such as calcium or magnesium. The exact mechanism whereby improved results are obtained inthis case is not well established, but I have found. that in some cases the'eflectiveness of the. electrode to emit impact electrons is very greatly increased by this treatment.

The novel features which I believe to be characteristic of my invention are set forth I with particularity in the appended claims. My invention itself, however, will best be understood by reference to the following description taken inronnection wlth the accompanyi'ng drawing in which Figs. 1 and 2 show perspective views partly brokenaway of two different forms of devices in which incorporated with satanode and is electrically connected to theinner screening gr1d'3. When such a devlce.

is used for amplification purposes and a fixed positive potential is applied'to the screening grid the effectiveness is somewhat reduced because of the fact that a certain percentage.

of the'electrons emitted from the cathodeare absorbed by the screening grid and do not reach the anode. To overcome this disadvantage I have found that the screening grid.

may be coated so as to emit im act electrons .trons emitted are equal in number to the pri mary electrons reaching the screening gri then the efi'ect'of this grid in reducing the current reaching the anode may be'entirely eliminated. Such a device may also be used effectively as a pliodynatron.

Fig. 2 shows a three-element device which may be used as a dynatron. This comprises the usual electron emitting cathode 6, grid electrode 7 surrounding the cathode and an anode or plate electrode 8 surrounding the grld and cathode.

In the manufacture of devices such as illustrated in Figs. 1 and 2, the electrodes which are to be treated to make them eflicient impact emitters, are before mounting in the tube coated with the selected compound of the metal having alkaline properties. This may be done in .a variety of ways; for example, if a borateis employed and the plate electrode is to-be coated, a bead of the borate may be formed on the grid support and this may be evaporated oflI' into the plate by electron bombardment of the grid. Any of the borates previously mentioned may be used in this way. One borate which I have found especlally suitable is lithium borate. This has the advantage that electrodes treated therewith have been found to emit practically one i act electron for every primary electnin rea hing them at a voltage'as low as 12 v0 ts.

Still another method which may be used to advantage 1n forming a coating is to mix the Y coating compound with a thin varnish such electrode in the bulb. When the coatin is as amyl-acetate-zapon varnish, applying this as a very thin coating on the electrode, and permitting it to dry before mounting the I have described or in other ways are greatly improved by supplying to the'space-adj acent the coated surface a metal vapor having 'vapor of magnesiumor calcium. In

as the Figs. 1 and 2, I have indicated a convenient way of supplying such avaporwhich consistsin securing to thegrid supports a quantity 9 of metal in the form of a paste. In the process alkaline properties, such, for example of evacuation the outer electrode or plate is first heated to fix the coating thereon and this heating may be carried. far enough to cause the vaporization of the metal on the grid support, thus furnishing the vapor directly to the space adjacent the coated surface While that surface is at a high temperature.

d Other ways of mounting the metal may be used-if desired, the essential features being that it is so placed that it may readily be vaporized and that the vapor will be supplied directly to the coated surface.

1 Some of the compounds which are effective in producing a good electronemission are comparatively unstable in the air, but are stable in the inside of the evacuated recepta- 'cle after the air has been exhausted therefrom. One example of such a compound is barium oxide. To overcome this disadvantage I have found that good results may be obtained by using barium peroxide to form the coating. By the subsequent heating of the coated electrode this peroxide is reduced to the oxide and good results may be obtained. i

I have not as yet determined the exact reason why the use of the metal vapor enhances the emitting properties of the coated surface. It appears likely thata partial reduction of the coating compound takes place which renders the coating more eflicient in emitting impact electrons and that the result ng compound is less stable than the original. In any event I have found that a surface which has been sensitized in the manner described loses its sensitivity if it is exposed to the air.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. An electron discharge device comprising an evacuated receptacle containing an electron emitting cathode and two other electrodes, one of said other electrodes having formed thereon a coating of a lithium'compound whereby the electrode thus coated is capable of serving as an eflicient emitter of impact electrons.

2. The method trode of an electron discharge device which consistsin coating the surface of said electrode with a compound of a metal having alkaline properties, mounting the electrode in a receptacle, evacuating the receptacle, heatof formin an efficient im- I pact electron emitting su ace on an elecing the electrode and supplyin to the s ace adjacent the surface a vapor o a metal ing alkaline properties.

3. The method of forming an eflicient im- GIV- pact electron emitting surface on an electrode of an'electron discharge device having a cathode, an anode and a grid which. consists in coating the surface of said electrode with a compound of a metal having alkaline properties, securing to the grid a quantity of a metal having alkaline properties, mounting the electrodes in a receptacle, evacuating the receptacle, and supplying sufficient heat to the anode to vaporize the metal having alkaline properties.

4. The method of forming an e flicient impact electron emitting surface on an electrode of an electron discharge device having a cath'-' ode, an anode, and agrid which consists in coating the surface of said electrode with a compound of a metal having alkaline roperties, I'nounting within the space en osed by the electrode a quantity of a metal having alkaline properties, mounting the'electrodes in a receptacle evacuatingthe receptacle, and

supplying suflicient heat to the anode to vaporize the metal having alkaline properties. In witness whereof, I have hereunto set my hand this 13th day of December, 1927.

HARRY C. THOMPSON. 

